How many years can a man grow in an hour and 20 minutes? At quarter to five on Saturday afternoon, Fin Smith, 22, looked awfully young to be leading England’s backline out at Twickenham. Slim, trimmed, and clean shaven, in crisp, freshly pressed whites, look close and you could almost see the lipstick on his cheek from the good-luck kiss his mother gave him before kick-off. Smith had played only seven Tests as a replacement, and a handful of minutes, coming into this game. He stood, flipping the ball from one hand to the other to burn off a little of his nervous energy as he waited for the referee to blow the whistle.

At half past six, the camera closed in on him again, 30 yards or so off from the same spot. He was standing over the ball as it sat on the tee, 15 metres or so out from the posts, muddy, bloody, sweaty, and bruised. It had been a hell of a match, a twisting, turning, helter-skelter set-to, and as Smith stood, drawing together his thoughts before the winning kick, he looked as if he had aged a couple of years and a couple of dozen caps. Le Crunch will do that to you.

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He had taken on the goal-kicking only moments earlier; the man whose place he had taken, Marcus Smith, had been doing it through the first 70 minutes. But Marcus’s touch had deserted him. He had missed a conversion, and then missed a penalty too, and Fin had taken on the job at the very moment when England couldn’t afford any more misses. His first conversion, far the harder of the two, won them a one-point lead with nine minutes to play. It was ripped away from them when Louis Bielle-Biarrey scored. When England scored one more, he faced a second, easier, kick to win it all over again.

When it was all over, after Fin had cleared the restart into touch, the stadium announcer named him man of the match, though you could hardly hear him over the chaos inside Twickenham. England fans had been waiting a very long time for a win like this one, and the place exploded as if someone had just knocked the top off a shaken bottle of champagne. Maybe Fin Smith will have had a glass himself. He sure earned one.

He can tackle, no doubt about that. France tested him out a few times in the first half by sending François Cros and Grégory Alldritt barrelling down his channel with the ball. Smith stopped them both. He took down Cros with a knee-high tackle that stopped the attack in its tracks, and it took two Frenchmen to stop him from going in for the turnover on Alldritt. The one he missed will stick with him, a flailing attempt to tap-tackle Antoine Dupont as he sprinted cross-wise across the pitch in the run-up to France’s opening try.

It took a little longer for him to show whether he could run at attack, too.

England certainly looked more orderly with him at No 10, no doubt about that. Marcus Smith often plays like a jazz musician who’s been accidentally recruited into a marching band, he can’t help himself but launch into another solo, freewheeling his way up, down, and around the scales while the men around him struggle to guess where he’s going to lead them next. England didn’t have that problem when Fin was in the line: he’s deft, square, and steady, with nothing too much more unpredictable than the occasional chip.

But orderly can also mean predictable, and in the first half he didn’t have much of a chance to show what he can do. When it finally came, their opening try was a desperate, ugly, scrambling thing off a five-metre scrum, a series of spilled passes which ended with Ollie Lawrence slapping down Thomas Ramos on his way through to the tryline, like a rhino who had finally lost his patience with the little bird that had been fluttering around his ears.

In the second half, though, England finally clicked. It helped that Fin was surrounded by men who play with him every week in club rugby at Northampton. Ollie Sleightholme has the happy knack of appearing in the line at just the right time to take a short pass, and Tommy Freeman must have been one of the few who knew where Fin was heading as he drifted back into the pocket, turned sideways, and hoisted a high, hanging kick into the far corner where Freeman was ready, and waiting to leap for it and score in the corner.

He made the last try, too, with a cute little slip pass to Elliot Daly as they burst through the French 22. He is the best young Smith to start at fly-half for England since, well, the last young Smith to start at fly-half for England. And while there will be plenty of ups and downs ahead, you suspect Marcus will have to get used to playing full-back, or filling a spot on the bench. He is prodigiously gifted, and showed a couple of thrilling touches in this match, but this was England’s best, and most cohesive, performance in a long time, and that’s no coincidence.